Glauber Costa wrote:> Turns out that most of the infrastructure we need to put two controllers in the> same hierarchy is by far already into place. All we need to do is not failing> when we specify two of them.>

You don't need to change anything to mount with 2 cgroup subsystems:

# mount -t cgroup -o cpu,cpuacct xxx /mnt

But you may want to revise and make use of the subsys->bind() callback, whichis called at mount/remount/umount when we attach/remove a controller to/froma hierarchy. It's the place you can check if two controllers are going tobe comounted/seperated.

> With this, we can effectively guarantee that by comounting cpu and cpuacct,> we'll have the same set of tasks, therefore allowing us to use cpu cgroup data> to fill in the usage fields in cpuacct.> > I decided not to stabilish any dependency between cgroups as Li previously did:> cgroups may or may not be comounted, and any of them can be combined (I don't> see a reason to prevent any combination).> > After testing and some trials, I could verify that the current mount behavior> plays well under the plans, so I didn't change it. That is:> > * If subsystems A and B aren't mounted, we can comount them.> * If subsystem A is mounted, but B is not:> * we can comount them if A has no children,> * we fail otherwise> * If subsystems A and B are comounted at a location, we can't> mount any of them separately at another point. We do can mount> them together.> * If subsystems A and B are comounted at a location,> * we can comount a third subsystem C, if they have no children> * we fail otherwise> > Paul,> > Please let me know if this is tuned with the idea you had in mind.> If this is okay, I patch that extracts usage from cpu cgroup data> in case of comount would follow.> > Signed-off-by: Glauber Costa <glommer@parallels.com>> CC: Paul Turner <pjt@google.com>> CC: Li Zefan <lizf@cn.fujitsu.com>> ---> kernel/cgroup.c | 4 ++--> 1 files changed, 2 insertions(+), 2 deletions(-)> > diff --git a/kernel/cgroup.c b/kernel/cgroup.c> index 1fd7867..e894a4f 100644> --- a/kernel/cgroup.c> +++ b/kernel/cgroup.c> @@ -1211,9 +1211,9 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)> set_bit(i, &opts->subsys_bits);> one_ss = true;> > - break;> + continue;> }> - if (i == CGROUP_SUBSYS_COUNT)> + if (opts->subsys_bits == 0)> return -ENOENT;> }>